In general, in order to charge portable terminals such as a cellular phone, a notebook, and a personal digital assistant (PDA), the portable terminals should receive electric energy (alternatively, power) from an external charger. The portable terminals include a battery cell storing the supplied electric energy and a circuit for charging and discharging (supplying the electric energy to the portable terminals) the battery cell.
An electrical connection mode between the charger for charging the electric energy in the battery cell and the battery cell include a terminal supply mode that receives commercial power and converts the received commercial power into voltage and current that correspond to the battery cell to supply the electric energy to the battery cell through a terminal of the corresponding battery cell.
The terminal supply mode is accompanied by the use of a physical cable or electric wire. Therefore, when a lot of terminal supply mode apparatuses are handled, a lot of cables occupy a significant work space and are difficult to arrange and external appearance is also not good. Further, the terminal supply mode may cause an instantaneous discharge phenomenon due to different potential differences among terminals, occurrence of damage and fire by foreign substances, natural discharge, deterioration of life-span and performance of a battery pack, and the like.
Recently, in order to solve the problems, a charge system (hereinafter, referred to as a wireless power transmission system) and control methods using the wireless power transmission mode has been presented. The wireless power transmission mode is also referred to as a contactless power transmission mode or a non-contact power transmission mode. The wireless power transmission system includes a wireless power transmission device that supplies the electric energy in the wireless power transmission mode and a wireless power reception device that receives the electric energy wirelessly supplied from the wireless power transmitting device to charge the battery cell.
In the terminal supply mode, a power transmission is performed through the terminal connection between a charger and a terminal, and the power transmission is stopped when the terminal is disconnected from the charger. On the other hand, the wireless power transmission system requires a coupling (magnetic induction and/or magnetic resonance) between the primary coil provided in a charger and the secondary coil provided in a terminal for charging owing to the non-contact charging characteristics, and the charger always transmits power to the terminal through the magnetic coupling. When performing a wireless power transmission by a charger in the wireless power transmission system, the charger should be able to stop the power transmission by detect the terminal to be removed from a charging area. As an example, a terminal may transmit a packet such as a control error packet indicating that the corresponding terminal is located in a charging area (or interface surface) to a charger, and the charger may determine the corresponding terminal to be removed from the charging area when the control error packet is not received for a predetermined period (e.g., 1.8 sec). However, when a terminal performs a battery charge through the wireless power reception, in some cases, serious load fluctuation may occur in the terminal (hereinafter, this is referred to a light load state), and owing to this, a distortion may occur in the packet transmitted to a charger from the terminal. In this case, although the terminal is located in a charging area, a problem occurs that the charger determines the terminal to be removed from the charging area and terminates the power transmission.